USDA evaluates prion-free cattle

Agricultural Research Service (ARS) scientists evaluated cattle genetically modified to not produce prions, and determined there were no observable adverse effects on the animals' health. These cattle can help in the exploration and improved understanding of how prions function and cause disease, especially with relation to BSE, said Edward B. Knipling, ARS administrator. In particular, cattle lacking

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Agricultural Research Service (ARS) scientists evaluated cattle genetically modified to not produce prions, and determined there were no observable adverse effects on the animals' health.

“These cattle can help in the exploration and improved understanding of how prions function and cause disease, especially with relation to BSE,” said Edward B. Knipling, ARS administrator. “In particular, cattle lacking the gene that produces prions can help scientists test the resistance to prion propagation, not only in the laboratory, but in live animals as well.”

Prions are proteins naturally produced in animals. An abnormal form of prion is believed to cause devastating illnesses called transmissible spongiform encephalopathies (TSEs), the best known of which is BSE.

ARS studied eight Holstein males developed by Hematech, Inc., a Sioux Falls, SD-based pharmaceutical research company. Led by veterinary medical officer Juergen Richt of ARS' National Animal Disease Center in Ames, IA, the evaluation revealed no apparent developmental abnormalities in the prion-free cattle.

Richt said, “The cattle were monitored for growth and general health status from birth up to 19 months of age. Mean birth and daily gain were both within the normal range for Holsteins. General physical examinations, done at monthly intervals by licensed veterinarians, revealed no unusual health problems.”

ARS, with assistance from Hematech and University of Texas researchers, evaluated the cattle using observation, post-mortem examination of two animals, and a technology that amplifies abnormal proteins for easier detection. Further testing will take at least three years to complete. — ARS Research Report, December 2006

Only 1% of U.S. cow-calf producers use the reproductive tract score (RTS) system to evaluate uterine development and ovarian activity of heifers.

Texas A&M University researchers conducted a two-year study to establish the value of the RTS system in an extensively managed, natural mating, 90-day breeding season program and to determine factors that may influence RTS. RTS utilizes a 1 to 5 scale, with 1 being the least developed and 5 being the most developed, with presence of a corpus luteum.

A total of 106 yearling Bonsmara-cross heifers were palpated and assigned an RTS just prior to start of breeding season. They were turned out with Bonsmara bulls at a bull-to-female ratio of 1:53 and 1:48 in years 1 and 2, respectively.

RTS was positively correlated with frame score, age, weaning weight and the weight of the heifer on the day of the RTS exam. For the two breeding seasons, pregnancy rate differed significantly for heifers with RTS 1 and 2 (62.5%) compared to heifers with RTS 3, 4 and 5 (91.2%). Females with an RTS of 1 conceived later during their first breeding season, weaned lighter first calves and had a lower fall body weight and body condition score each year, compared to heifers with an RTS of 3 or higher.

The authors say yearling heifers with an RTS of 1 immediately prior to their first breeding season should be culled, and that reproductive performance is reduced in heifers with a RTS of 2. — Rathmann et al, 2006, Southern Section ASAS, Abstract 48

Expected progeny difference (EPD) for milk is an accurate indicator of milk production and calf performance.

In a long-term study, Oklahoma State University researchers mated crossbred cows to Angus or Hereford bulls either very high or very low for milk EPDs. Heifers from these matings were born over a five-year period (1989-1993). When the heifers were six, seven and eight years old, milk production was measured, and weaning weights of their calves compared.

Cows sired by high milk (HM) bulls produced significantly more milk than cows sired by low milk (LM) bulls in all months except for the seventh month.

Cows sired by HM bulls had 30.5-lb. heavier calves at weaning than those sired by LM EPD bulls.

Compared to LM cows, there was a tendency for HM cows to have longer calving intervals, later calving dates and lower calving percentages than LM cows, but the differences weren't statistically significant.

The results indicate HM EPD bulls sire cows that produce more milk and wean heavier calves than cows sired by LM EPD bulls. It may, however, come at the expense of body condition and reproductive efficiency.Erat and Buchanan, Oklahoma State University Beef Research Report, 2005